A thyroid nodule with poorly defined borders may be malignant, but it is not 100%. Because there are many other indicators to determine the benignity or malignancy of a thyroid nodule, they must be combined. For example, the shape of the nodule, its border, internal echogenicity, pericardial bands, the presence of a halo, the presence of cystic changes, the pattern of calcifications inside the nodule, the presence of infiltration of surrounding tissues, the presence of lymph node metastases, etc. If the boundary of a nodule is unclear, jagged, with hypoechoic internal echogenicity and posterior attenuation with punctate calcification, this can be considered as thyroid cancer, and thyroid cancer is usually rich in blood flow signal, which is high speed and high resistance arterial blood flow.